Is Rainwater Harvesting Legal in Colorado?

Yes — with limits.

Most Front Range homeowners on city water can collect roof runoff in two rain barrels, 110 gallons combined, for outdoor use on the same property. No Division of Water Resources (DWR) permit. That is the everyday two-barrel rule.

Want a big cistern? That is a different route. It only opens if the property has — or can qualify for — an exempt or small-capacity well, and only after you get a rooftop precipitation collection permit. On a typical Denver or Littleton municipal tap, that larger route is closed. Stick to the barrels.

This page tracks the Colorado DWR rainwater page (https://dwr.colorado.gov/services/water-administration/rainwater-storm-water-graywater) and the CSU Extension rainwater guide (https://extension.colostate.edu/resource/rainwater-collection-in-colorado/). Practical orientation for homeowners. Not legal advice, and we are not DWR.

Two ways Colorado lets you collect roof water

Precipitation falls under Colorado’s priority system of water rights. The state carved out two household allowances for limited roof collection. The two rules work separately. DWR says a home that qualifies for the well-based permit can collect under it in addition to the 110-gallon barrel allowance.

The two-barrel rule comes from House Bill 16-1005 (https://leg.colorado.gov/bills/HB16-1005), now C.R.S. § 37-96.5-103 (https://colorado.public.law/statutes/crs_37-96.5-103): no more than two rain barrels, 110 gallons combined, from the rooftop of a single-family residence or a multi-family residence with four or fewer units, used outdoors on that same property. Drinking and indoor household use are not allowed under this article. DWR requires no permit inside those limits.

The larger, well-based route is separate. If the residence has, or can qualify for, an exempt or small-capacity well, more storage may be possible — but only after form GWS-78 and a rooftop precipitation collection permit. Uses follow the well permit. See DWR well permitting (https://dwr.colorado.gov/services/well-permitting) for forms and records.

Barrels do not authorize extra tanks. On a Denver or Littleton city tap, the two-barrel rule is usually the only live option.

Why rain barrels used to be illegal in Colorado

Colorado runs rain through its water-rights system. People who claimed water first get first use, and rain feeds the streams they draw from. So catching roof rain counted as taking their water, and for most homes it was illegal until 2016. Today most homes can use two rain barrels, 110 gallons total, outdoors on the same property, no permit.

Who owns the rain? Not you, and not your neighbor either

Colorado's constitution calls stream water "the property of the public," dedicated to the use of the people and "subject to appropriation." It adds: "Priority of appropriation shall give the better right." Nobody owns the water outright. People hold rights to use it, in line, and whoever put it to use first gets served first.

Source: https://law.justia.com/constitution/colorado/cnart16.html

How a rain barrel got tangled up in that

DWR says precipitation, "including snow, rainwater and stormwater, is administered within the Priority System of water rights." Rain off your roof soaks into the ground or heads toward a creek. Farms, ranches, and cities downstream hold rights to that water.

CSU Extension explains the catch. To protect senior rights holders, storing water is allowed only when every water right in the basin is satisfied. A homeowner has no practical way to know when that is. Before House Bill 16-1005, CSU says, rainwater collection was not permitted except in specific circumstances.

Farmers and ranchers fought the 2015 barrel bill. They argued rainwater falls under prior appropriation because it runs off into groundwater and rivers. A Fort Morgan dairy operator told legislators barrels "would allow people to steal water from my appropriation." That's one side's view, as Colorado Politics reported it.

Source: https://www.coloradopolitics.com/2015/05/06/rain-barrel-bill-dies-on-calendar/

How the law loosened: 2009, 2015, 2016

- 2009: Senate Bill 09-080, effective July 1, 2009, let homes with an exempt or small-capacity well, or that qualify for one, collect roof water with a state permit. That's today's well-based permit (form GWS-78).

- 2015: House Bill 15-1259 would have allowed two 55-gallon barrels. It died in the Senate in the last days of the session.

- 2016: House Bill 16-1005 was signed May 12 and took effect August 10, 2016. That's the two-barrel rule.

- 2025: House Bill 25-1106 would have removed the limits. It was postponed indefinitely on February 13, 2025.

Sources: https://content.leg.colorado.gov/sites/default/files/digest2009.pdf and https://leg.colorado.gov/bills/HB16-1005

The deal the 2016 law struck

The two-barrel law didn't overturn the water-rights system. It says water "is subject to the doctrine of prior appropriation," and that "the use of a rain barrel does not constitute a water right." It also says "the state engineer may curtail rain barrel usage." Per CSU, that could happen if a water-right holder proves barrels cut into the water they're entitled to.

So you can use the barrels. You don't own that water the way a farmer owns a decreed right. The state keeps the power to curtail barrels if they ever injure a senior right. That's why the two-barrel rule below says capture is not a water right.

Sources: https://colorado.public.law/statutes/crs_37-96.5-101 and https://colorado.public.law/statutes/crs_37-96.5-103

What that means for your house today

For most homes: two rain barrels, 110 gallons total, used outdoors on the same property. No permit. Anything bigger needs the separate well-based permit, and that's closed if your water system serves more than three single-family homes. That rules out most Denver and Littleton city taps. Why a bigger tank isn't a simple hardware swap: https://sunhousesystem.com/barrel-vs-cistern

The two-barrel rule: 110 gallons, outdoors

C.R.S. § 37-96.5-103 (https://colorado.public.law/statutes/crs_37-96.5-103) and the definitions in C.R.S. § 37-96.5-102 (https://colorado.public.law/statutes/crs_37-96.5-102) set the rules:

- Who qualifies: A building used primarily as a single-family residence, or a multi-family residence with four or fewer units. DWR treats each home in a duplex, triplex, or townhome as a single-family residence.
- Storage cap: Up to two rain barrels with a combined capacity of 110 gallons or less. You may fill and refill them through the year. The cap is storage volume, not a seasonal gallon quota.
- Container type: Aboveground containers with sealable lids, fed from a rooftop downspout. A buried cistern is not a rain barrel under this statute.
- Where you can use it: Outdoors on the same residential property — primarily lawn and garden irrigation.
- What this rule does not allow: Drinking water and indoor household purposes under this article.
- DWR permit: None for a true two-barrel setup.

Sealable lids keep mosquitoes out and match the statute. CSU also recommends emptying barrels regularly and disconnecting them if you will be away more than a week. A first-flush diverter is good practice; the lid is what the law requires.

Design for irrigation. Agency materials can differ on edge outdoor uses such as animals or hot tubs — confirm with DWR before you count on a barrel for those.

Capture under the two-barrel rule is not a water right. The State Engineer may curtail use if a water-right holder shows injury.

Larger storage after a well-based permit

You do not buy your way into a bigger tank. DWR limits that route to a residence that has, or can qualify for, an exempt or small-capacity well. Eligibility is DWR’s call when you apply.

Hard exclusion: if a water system serving the home (municipal or shared well) supplies more than three single-family dwellings, the larger route is not available. That covers most Denver and Littleton city-tap homes. The two-barrel rule stays open. A large cistern marketed as a “rain barrel” does not match the statute.

Where the property does qualify:

1. Confirm exempt / small-capacity well status.
2. Register an unregistered well if needed (GWS-12).
3. Apply with GWS-78 and wait for the permit before collecting beyond the barrel allowance.

On that route, DWR puts no stated gallon cap on roof collection from the residence. Storage may be barrels or other structures. Use is capped by the well permit. Listing household use on a well permit does not make roof water safe to drink.

HOAs, downspouts without barrels, and HB25-1106

An HOA cannot ban rain barrels that comply with the statute. It may set reasonable aesthetic rules — backyard placement, a color that blends in. Appearance rules are allowed. A disguised ban is not.

Sending a downspout onto a garden without storing the water is ordinary drainage, not regulated harvesting, according to CSU. Splash block = drainage. Barrel or cistern on that downspout = collection.

House Bill 25-1106 (https://leg.colorado.gov/bills/HB25-1106) would have removed the gallon limit and use limits at small residences. It did not pass (postponed indefinitely, February 2025). The 110-gallon limit remains.

Decision guide: Denver and Littleton city taps

Start with the tap, not the tank size you saw online.

Your situation — What usually applies
Single-family, duplex, triplex, or townhome on Denver / Littleton municipal water — Two barrels, 110 gal combined, outdoor irrigation, no DWR permit
Proposal for a large cistern on that same city tap — Not under the barrel rule; the well-based route is usually closed by the “more than three dwellings” rule
Exempt or small-capacity well on the property (or you are ready to ask DWR if one could qualify) — Larger storage may be available — GWS-78 before collecting more than 110 gallons

Plan on a garden assist, not a full summer of lawn water. CSU estimates each full 110 gallons covers about 180 square feet of garden or lawn at about one inch, and that a typical setup fills completely about 10–15 times a growing season. You will still need supplemental irrigation most years.

Untreated roof water is not drinking water. Keep lids sealed.

What we install for Front Range homes

Sun House System LLC installs rainwater systems through its Rain Harvest Solutions division. We work Front Range homes every week.

For the two-barrel setup, we help with sealable lids, a workable downspout connection, overflow kept off the foundation, and placement that can meet reasonable HOA aesthetics. See rainwater harvesting (https://sunhousesystem.com/rainwater-harvesting) and about Sun House System (https://sunhousesystem.com/about).

For larger storage, we talk roof area, storage, screening, and layout only when an exempt or small-capacity well is already in play — or when you plan to ask DWR whether one could qualify. We never promise DWR approval. We do not treat a large cistern as the city-tap default. If the well-based route is unavailable, the legal design stays the 110-gallon outdoor barrel setup.

Ready to see what fits your roof and yard? Call for a site visit, or request an estimate.

Frequently asked questions

Is rainwater harvesting legal in Colorado?

Yes, with limits. Most qualifying homes may use two barrels totaling 110 gallons outdoors with no DWR permit. More storage requires a precipitation permit tied to an exempt or small-capacity well.

Why were rain barrels illegal in Colorado?

Because Colorado treats rain as part of the water supply that people with water rights use in priority order, and catching it was seen as taking water out of line. That changed for most homes in 2016. Now most homes can use two rain barrels, 110 gallons total, outdoors on the same property, with no permit.

When did Colorado legalize rain barrels?

In 2016. House Bill 16-1005 was signed May 12, 2016 and took effect August 10, 2016. It allows two rain barrels, 110 gallons total, for outdoor use on the same property, with no permit.

Do I need a DWR permit for two rain barrels on my Littleton house?

Not under C.R.S. § 37-96.5-103 (https://colorado.public.law/statutes/crs_37-96.5-103): two barrels, 110 gallons combined, residential rooftop, outdoor use on the same property, no drinking or indoor use under this article. Storing more than that takes the well-based permit, and a home on Littleton city water can't get it, because the water system serves more than three homes.

Can I drink the water from my barrels, or run it to a sink?

No under the two-barrel rule. CSU is clear: untreated roof water is not drinking water. Indoor use shows up only on the well-based route when the well permit allows it — and that still does not make the water potable without proper treatment.

I’m on Denver city water. Can I put in a big cistern for the garden?

Almost certainly not on the well-based route. DWR closes that path when the supplying system serves more than three single-family dwellings. Legal collection on a typical city tap is two aboveground barrels, 110 gallons combined, used outdoors on your property.

My HOA says no rain barrels. Are they allowed to ban them?

They cannot ban barrels that comply with the statute. They may set reasonable placement and appearance rules.

Did Colorado get rid of the 110-gallon limit in 2025?

No. HB25-1106 did not pass (postponed indefinitely in February 2025). The two-barrel, 110-gallon outdoor limit remains in force.

Who owns the rain that falls on my roof in Colorado?

No one owns it outright. The state constitution makes stream water public property, and people hold rights to use it in priority order. DWR runs rain through that same priority system, which is why roof collection has limits.

Is my rain barrel a water right?

No. State law says "the use of a rain barrel does not constitute a water right." You can use what your barrels catch, within the 110-gallon limit. You can't claim that water the way someone with a decreed water right can.

Can the state make me stop using my rain barrels?

Yes, in theory. The State Engineer can curtail barrel use if a water-right holder shows the barrels injured their right. The 2016 law spells out that procedure, and it rests on a finding of material injury.

Was collecting rainwater completely illegal before 2016?

No. Starting July 1, 2009, homes that had or qualified for an exempt or small-capacity well could collect roof water with a rooftop precipitation collection permit from DWR. That's still the well-based permit today (form GWS-78). It's closed to homes on a water system that serves more than three single-family homes.

How much garden will 110 gallons actually water?

CSU’s rule of thumb: about 180 square feet per full 110 gallons at roughly one inch of water. Expect roughly 10–15 complete fills in a growing season on a typical Front Range setup. That helps a bed or a small lawn patch; it does not replace your hose for the whole yard.

Sources

- Colorado DWR rainwater page (https://dwr.colorado.gov/services/water-administration/rainwater-storm-water-graywater)
- CSU Extension rainwater guide (https://extension.colostate.edu/resource/rainwater-collection-in-colorado/)
- C.R.S. § 37-96.5-103 (https://colorado.public.law/statutes/crs_37-96.5-103)
- C.R.S. § 37-96.5-102 (https://colorado.public.law/statutes/crs_37-96.5-102)
- House Bill 16-1005 (https://leg.colorado.gov/bills/HB16-1005)
- House Bill 25-1106 (https://leg.colorado.gov/bills/HB25-1106)
- DWR well permitting (https://dwr.colorado.gov/services/well-permitting)
- Colorado Constitution, Article XVI (Justia): https://law.justia.com/constitution/colorado/cnart16.html
- C.R.S. § 37-96.5-101: https://colorado.public.law/statutes/crs_37-96.5-101
- Senate Bill 09-080, 2009 Digest of Bills: https://content.leg.colorado.gov/sites/default/files/digest2009.pdf
- Colorado Politics, "Rain barrel bill dies on calendar" (May 6, 2015): https://www.coloradopolitics.com/2015/05/06/rain-barrel-bill-dies-on-calendar/

Sun House System LLC, Rain Harvest Solutions division. We are not DWR. Confirm with DWR before storing more than the barrel allowance.